1. Field of the Invention
The invention relates generally to rocket and missile launchers and, in particular, to a positive detent and release mechanism for a rocket propelled missile.
2. Description of the Prior Art
Rocket launchers are well known in the prior art. Each generally consists of a light weight, relatively thin aluminum launch tube having a diameter which is slightly larger than that of the body of the rocket. The launch tube may also be made of a composite material such as fiber glass or resin impregnated paper. The length of the launch tube is usually greater than that of the rocket. A plurality of launch tubes may be assembled together into a pod which is carried on pylons beneath an airplane's wing or along the fuselage of a helicopter. The firing sequence of a group of rockets is generally one at a time so that the total heat generated by the rocket motors within the pod at one time is kept at a minimum. Also, rocket collisions in free flight are avoided. Alternatively, the missile or rocket may be launched from a rail.
In addition to the standard launcher having a flat face, an experimental supersonic rocket launcher has been fabricated for an F-4 Phantom jet which carries eighteen 2.75-inch folding fin aircraft rockets in individual aluminum launch tubes. The individual launch tubes are spaced symmetrically about a central axis. The launcher consists of three major sections. The forward section contains 18 aluminum launch tubes and provides the basic aerodynamic shape and main structural integrity and strength of the launcher. The middle section contains the electrical firing circuitry and rocket retention mechanisms. The tail section of the launcher is a hollow aerodynamic fairing designed to reduce base drag. The launcher features a lightweight composite structure consisting of a foam encapsulated, integrally bonded aluminum tube matrix in combination with a glass fiber reinforced epoxy laminated structural system covered by an outer skin.
It is important that each of the rockets be fired properly and that each exits its respective launch tube without damaging it. In practice it has been acceptable to have a few launch tubes in a pod that are inoperative. If more than these launch tubes should be damaged in firing their cargo, the entire launcher would have to be discarded. Thus, every damaged launch tube is a potentially expensive occurrence.
The rocket, as configured for the field, has the rear stabilizer fins folded backwards so that they extend beyond the rear of the rocket body and their leading edges lie within the projection of the body's circumference. After folding the fins, a rectangular plastic fin retainer is attached to the fin tips to keep them in place. A circular metal contact disc is disposed on the face of the plastic retainer facing away from the fins. An electrical wire connects the contact disc with the firing mechanism within the rocket. The fire signal is applied to the rocket through the metal contact disc. The body of the rocket is "grounded" through the retainer's contact with the rocket.
In loading the rocket into its launch tube, referred to as "up loading", the rocket is slid into its launch tube until a circumferential ridge at the aft portion of the rocket body engages the detent/release mechanism. The contact disc at the same time engages an igniter contact arm through which the "fire" signal is conducted to the rocket motors. Up-loading of most prior art launch tubes requires a substantial amount of force. For example, it may require a 250 pound force to release the rocket from the launch tube and, conversely, it may require that same amount to engage the detent, depending upon the configuration of the particular release mechanism. It is not unusual to see technicians literally flinging the rockets into the launch tube in order to engage the detent mechanism.
In flying a mission, the rocket detent is required to perform several functions. It must keep the rocket in place at all times irrespective of the craft's attitude and the forces which are exerted on it. For instance, during aerobatic maneuvers and during landings, great forces and stresses are placed on the detent mechanism which is expected to restrain the rocket. In carrier landings where arresting lines and hooks are used to stop a jet, it has been calculated that forces in excess of 9 g's are generated, which are also exerted on the detent mechanism. In catapult take-offs, forces of 6 g's have been calculated. If the detent mechanism malfunctions, the rocket could be separated from its launch tube, possibly causing extensive damage to the craft, or persons and equipment near the craft.
When the rocket motor is fired, it is expected that within a predetermined time, or within a predetermined thrust force of the rocket, the release mechanism will be actuated and the rocket will exit the launch tube. If the release mechanism should malfunction and the rocket is not released, called "hangfire", the launch pod could sustain substantial damage as well as possible damage to the aircraft structure. A hangfire in a helicopter launched rocket is especially dangerous because handling characteristics are more easily affected by outside forces due to the lighter mass of the helicopter. If a rocket fails to exit the launch tube within a few seconds of the thrustor being fired, the launch tube may sustain substantial fire damage possibly making it inoperable for future use. Certain materials, such as fiber glass, composite or aluminum within the firing end of the rocket launcher pod cannot withstand continuous temperatures associated with the rocket motor propellant burning characteristics without damage. In addition, ejected fragments from the failed tube may present a hazard to the aircraft. Notwithstanding the fact that most rocket pods are disposable armament, if a sufficient number of launch tubes are damaged due to the rocket's flaming within the tube, the pods may have to be discarded prematurely. Depending upon the number of launch tubes in a particular pod, a certain number of damaged launch tubes may be acceptable. However, when the number of damaged launch tubes exceeds a predetermined percentage of the total, then the entire pod must be discarded. Generally, these otherwise disposable rocket launch pods may be used almost indefinitely so long as the rockets and detent mechanism do not malfunction. Thus, many firings may be obtained from an individual pod.
The fin retainer is blown away by the action of the thrustors and as the rocket exits its launch tube, the folded back fins are deployed to their proper positions within a few feet of the rocket leaving the tube. Surprising results were found in tests conducted on a number of launch tubes using prior art release mechanisms, and it was found that the release forces required for each succeeding test tended to be substantially lower than the preceeding test. In other words, each subsequent rocket launch occurred earlier than the last, due to the mechanism becoming weakened from the prior firing. Eventually, the launch tubes, become unusable due to the release mechanisms being ineffective and dangerous.
A prior art detent mechanism used extensively provides a longitudinal restraint to a rocket by means of a notched detent member which interfaces with the circumferential ridge aft of the rocket motor bourrelet. The detent member is held down in place, against the circumferential ridge, by a leaf spring to preclude inadvertant release due to vibration or shock loads. At launch, the detent is released by the rocket motor thrust overriding the detent restraining force. In the examination of this prior art detent mechanism after firings, it was found that the detent material had undergone permanent deformation such that the notch had become elongated until only a small ridge was left. This ridge was found to be unable to properly restrain future loads. Another shortcoming of such prior art detent mechanisms is that the release depends upon columnar bending forces which are essentially unpredictable. In some pod configurations, it is generally required that a rocket be released by forces in the range of 175 to 280 pounds. However, in several tests it was found that it took more than the maximum prescribed force to release the rocket. It appears that the erratic forces required to release the rocket is an inherent characteristic of that prior art detent. In addition, many factors increase the variation. Such excessive forces could result in damage to the pod, the mounting structure or the aircraft.